Physically compatible agrochemical mixtures exhibit better pest management. These mixtures show multifaceted advantages than when applied individually. But achieving physical compatibility becomes major challenge while combining two or more agrochemicals. The problem of physical compatibility further aggravates when low melting active ingredient needs to be formulated with another active ingredient.
Some of the low melting active ingredients like pyrethroids (synthetic pyrethrins) are known to control agricultural insect pests on crops. Pyrethroids interfere with the ionic conductance of nerve members by prolonging the sodium current. This stimulate nerves to discharge repeatedly causing hyper-excitability in poisoned animals.
Active ingredients having pest control ability selected from fungicides such as strobilurins and insecticides such as organophosphates are advantageous to be co-formulated with low melting actives for better pest management. Some of these active ingredients are moisture sensitive and thus rapidly degrade while processing into a suitable formulation or composition.
Moisture sensitive active ingredient, such as Acephate (organophosphate) is a systemic and contact insecticide of moderate persistence with residual activity lasting about 10-15 days. Acephate, being highly prone to moisture and is not very stable in conventional pesticidal formulations, such that a vigorous decomposition of acephate in conventional formulations takes place depending on storage conditions and, as a result, the insecticidal activity of acephate sometimes cannot be fully utilized.
Though it is advantageous to co-formulate moisture sensitive active ingredients with low melting active ingredients for better pest management, it is challenging to develop stable as well as efficacious formulation.
There are large number of low melting active ingredient formulations that are being used for combating pest attacks on plants. Available formulations include emulsion concentrates (EC), aqueous emulsion (ES). But, these formulations cannot be prepared when another active ingredient is moisture sensitive and is prone to water.
Dry granular formulations such as water dispersible granules of low melting active ingredients like pyrethroids have been known and are in practice. The conventional ways of preparing granules include methods like extrusion granulation wherein a dough is prepared using water which is then subjected to granulation. Another way of preparing the granules is to make a slurry in water and then subject it to spray drying.
When the low melting ingredients like pyrethroids have to be combined in a pre-mix with a moisture sensitive ingredients like organophosphates, it becomes a challenge to do so as the moisture sensitive ingredient cannot be granulated using water. Moreover, rise in temperature during extrusion granulation may melt low melting actives. Once granules are extruded and kept in ambient conditions, low melting actives become solid again. This solid-liquid-solid phase change result into altered morphology leading to changed crystal form, or a layering of the ingredient on the surface of the granules or the granules may become hard. This granular composition when applied in fields by way of dilution/tank mixing yields unsatisfactory non-uniform dissolution (dispersion) of the composition with lack of homogeneity in the resulting mixture and prevents distribution of constant concentration of the desired active in the fields. Lack of dispersion in desired manner will reduce the availability of the active ingredient for the intended use as pesticide thereby making the product ineffective.
Another method which is employed for making a pre-mix of such ingredients is to dissolve the low melting ingredient into suitable solvent and then mix it with the moisture sensitive ingredient and then granulate. This method requires use of large amount of organic solvents which are not only expensive but are not environmentally friendly. The granules may have to be subjected to longer drying period in order to remove the traces of solvent from the final product.
WO2015142609 A1 discloses micro particles comprising water soluble organothiophosphate (e.g. Acephate) and pyrethroids (e.g. Bifenthrin). The invention presents effective odor control solution by adding odor-absorbing and odor-masking components.
US20090208423 discloses synergistic insecticidal composition comprising imidacloprid, lambda-cyhalothrin and a conventional agriculturally acceptable carrier or excipient formulated as an aqueous formulation or dry based formulations. The application also discloses a process of mixing the actives and the excipients to obtain a homogenous mixture of all ingredients, which is micronized and granulated to yield the granular formulation. While this process is acceptable, micronizing the inert fillers in which liquid active is absorbed can pose several problems since the liquid naturally tends to come out during fine grinding. Such compositions obtained do not generally exhibit good dispersibility and shelf life especially since the low melting actives undergoes a phase change during the ambient storage temperatures (−5 to 50° C.) leading to caking and crystal growth.
Indian Patent Application No. 1709/MUM/2010 discloses synergistic insecticidal composition of acephate and bifenthrin wherein bifenthrin technical dissolved in solubilizer was sprayed onto the mixture of acephate technical and formulation auxiliaries to obtain granules. The problem with this method is large amount of solubilizer required by bifenthrin that imparts softness to the finished granules. In this case, high loading of active ingredients is not possible due to undesirable softness of granules.
WO2002076213 A1 discloses a pesticidal composition comprising specified pyrethroids and organophosphates in a weight ratio of 50:1 to 1:5 wherein a pyrethroid is selected from deltamethrin, fenvalerate, esfenvalerate, cyfluthrin, beta-cyfluthrin and bifenthrin, and an organophosphate insecticide selected from triazophos, profenofos, chlorpyrifos-methyl, monocrotofos, acephate, methamidophos and diethyl 1-phenyl-1H-1,2,4-triazol-3-yl phosphate.
Although various efforts had been taken in the past to develop a stable pesticidal composition containing low melting active ingredients and moisture sensitive active ingredients, there is still a long felt need to develop an alternative, simple and an efficient product and a process for developing the stable pesticidal compositions of these active ingredients. Also, there is a need for developing such formulations, wherein the formulation overcomes drawbacks of the prior art and exhibits increased stability with respect to degradation of moisture sensitive actives and dispersibility/suspensibility of low melting active ingredient in combination. The physical stability of the formulation during storage/use is a key problem in the art and the same is to be addressed.